The present invention generally relates to electric water heaters and, more particularly, to a flow-through water heater and control system therefor.
Electric flow-through water heaters are commonly employed for use in heating circulating water for use in a spa/hot tub and other applications. Electric flow-through water heaters commonly employ an electrical heating element disposed in a metallic vessel such that the heating element is in contact with the flow of water to provide heat exchange to the water as it flows by the heating element. In addition, a water pump is generally used to continuously circulate water through the heater vessel. In the conventional water heating system, a thermostat is typically disposed within the hollow of the vessel to sense the temperature of the heated water, and the heating element is generally controlled based on the sensed water temperature. In one approach, an electrical resistance heater having a positive temperature coefficient of resistivity is employed to act as the temperature sensor as disclosed in U.S. Pat. No. 4,736,091. According to most conventional approaches, the electric heater is controlled in response to the sensed temperature of the water to maintain a desired water temperature.
In addition to controlling the heating element to maintain a predetermined water temperature, it is also desirable to ensure adequate operation of the water heater to prevent overheating or other abnormal conditions that could adversely affect the water heater. In particular, overheating could occur in the event that there is an inadequate amount of water present in the heater vessel due to an abnormally low water level, or in the event there is inadequate water flow through the heater vessel, such as can be caused by failure of the water pump or restricted water flow. In the event that such adverse conditions occurs, it is generally preferred to shut off the water heater to prevent damage to the water heater system. The earlier the detection of a potential problem, the more likely the prevention of any damage to the system.
It is therefore desirable to provide an electric heater and control therefor that quickly and efficiently detects and responds to abnormal conditions. In particular, it is desirable to provide an electric heater and control system that is able to quickly detect a dry fire condition and take corrective action to prevent adverse effects. It is also desirable to provide an electric flow-through water heater and control system that quickly detects a stagnant water condition and takes corrective action to prevent adverse effects. Yet, it is further desirable to provide an electric heater and controller that allows for use of a polymeric heater vessel.